The present invention relates to a metallurgical melting process and a direct current arc furnace for its application. More particularly, it relates to a metallurgical melting process and a direct current arc furnace for its application in which passage of the current takes place across the metal mass to be melted, between a moving vault electrode placed above the metal mass and maintaining an electric arc with the latter and a hearth electrode implanted in the wall (generally at the bottom of the furnace) and in permanent contact with the mass to be melted in order to assure the return of the current.
Metallurgical melting processes and direct current arc furnaces for its application of the above mentioned general type are known in the art.
The use of arc furnaces operating on direct current has, among other things, the advantage of making possible high capacities, adapted to the treatment of sizable metal masses in large-sized furnaces.
However, difficulties can occur in the starting phase of melting on a divided solid charge (scrap metal). To understand them well, it is necessary to recall briefly the operation of an electric arc furnace.
The method of operation, perfectly standardized and common to all furnaces of that type, regardless of the nature of the current which feeds them (alternating or direct current) is as follows:
After having put the charge to be melted in the furnace, the value electrodes are slowly dropped into the charge to nearly the bottom. The electrodes thus dig a hole by locally melting the solid material coming in contact with them during their descent. The molten metal percolates between the still solid fragments and forms on the bottom a puddle of molten metal "hot heel". Once the electrodes are completely descended, the starting phase is over and they are slowly brought up again, while maintaining an electric arc between the tips of the electrodes and the puddle of molten metal which grows as melting progresses. The latter is completed when the electrodes reach their stable top position.
On alternating current applications, several vault electrodes with opposite polarities are used. They are mounted relatively close to each other at a constant distance. Under these conditions, melting is started off easily, since the electric current is looped on two electrodes across the solid metal material lying between them.
On the other hand, on direct current applications, the vault electrode is too far from the hearth electrode in the starting phase to allow the furnace to operate at full capacity, as would be desirable in the melting period for maximum efficiency of the equipment.